Solid surfaces in contact undergo relative motion experience wear due to friction. Wear is the progressive loss of material due to interacting surfaces in relative motion. Excessive wear often leads to premature failure of a part. Intrinsic material properties such as hardness, strength, ductility, etc. are important factors that determine the wear resistance of the material. The surface condition of interacting parts also play an important role in the amount of wear experienced by the part. When two surfaces are in contact, surface roughness causes contact to occur at discrete contact areas. The localized contact increases local stresses, and thereby wear, at these contact areas. Therefore, smooth surfaces typically experience less wear than rough surfaces. Solid surfaces, irrespective of their method of formation, generally contain surface irregularities. Therefore, a part may be subject to some post-fabrication finishing or polishing operations to reduce its surface roughness before being used in an application where wear resistance is a consideration.
In some applications, considerations other than wear resistance (such as, electrical or thermal conductivity) may drive the selection of material for a part that may be used in a wear related application. A power conducting rail (“power rail”) that delivers power to a moving device is an example of an application where the rail may be fabricated from aluminum due to its high electrical conductivity. Examples of such applications include conductor bars that deliver power to moving equipment such as overhead cranes and other material transportation systems, and third rails that deliver power to electric trains. The moving devices (crane, material handling system, train, etc.) have metal contact blocks called “shoes” that make contact with a surface of the power rail during operation. Therefore, surfaces of the power rail that interact with the shoes may be subject to wear. To reduce wear related failures, a strip of material (or a cap) made of a sufficiently wear resistant material (such as stainless steel) may be attached to the surface of the power rail that interacts with the shoes. To reduce wear of the rail and the shoes, the surfaces of the cap that may be subject to wear may be smoothed before the cap is attached to the rail.
EP535865 B1 (“the '865 patent”) discloses a rail with an aluminum main body and a stainless steel cap. The stainless steel cap is welded to the main body to form a surface that will contact the wheels of a train. In the '865 patent, the cap is separately formed and mechanically bonded to the aluminum rail. Since the cap is separately formed, the surface of the cap may be finished to reduce its surface roughness before being welded to the rail. While the stainless steel cap of the '865 patent may provide wear resistance to the aluminum rail, it has disadvantages. For instance, the fabrication and finishing of the cap and the welding of the cap on the rail may require capital equipment investment, and therefore increase costs.
The disclosed coated power rails are directed at overcoming these and/or other shortcomings in existing technology.